The story of the English law on murder is almost as perverse as many of the crimes it was designed to punish. The actual sentences for the crime have moved on some way since the 17th century, but the concepts have not.

Some of the complexity of the law on murder is unavoidable. The range of circumstances in which one person kills another are extraordinary, and it is the law's job to assign appropriate levels of blame for a diverse range of crimes.

The most obvious way of dividing this up is based on intention – what Coke describes as "malice prepense". In 2006 the Law Commission proposed US-style offences of first- and second-degree murder, depending on the seriousness of the killer's intent. Without this kind of reform, its report said, the law would remain "a rickety structure set upon shaky foundations". "Some of its rules have been unaltered since the 17th century," it continued, "even though it has long been acknowledged that they are in dire need of reform."

The extent of this acknowledgment was clear yesterday, when the director of public prosecutions, Keir Starmer, joined the voices of countless judges, law lords and the president of the supreme court, Lord Phillips, all of whom have called on the government to follow the US system and create varying degrees of murder.

All have argued – rightly – that not all cases where a person intended to inflict grievous bodily harm should be dealt with in the same way as intentional murder. Whether one category of murder should be downgraded, a proposal the DPP lent his support to yesterday, or a category of manslaughter upgraded – as Paul Mendelle, the former chair of the criminal bar association, has proposed – some kind of distinction needs to be made.

But the problems with murder go further than this. The doctrine of joint enterprise, also singled out for reform by the Law Commission in the past, is a related anomaly. Under the current law, the intention to cause grievous bodily harm where someone is then killed can allow scores of people to be convicted of murder. This principle is increasingly being used to round up groups of young people involved in gangs and sentence them to life for crimes they did not literally commit.

And another is mercy killing – an issue that refuses to go away. Although the implementation of the law on assisted suicide is for the moment settled, after the DPP published a code following a successful legal challenge by MS sufferer Debbie Purdy last year, mercy killings can and do result in murder convictions. Reforming the law to first- and second-degree offences would not address this, because these are cases where a partner or relative does intend to kill.

Hundreds of pages of carefully reasoned and consultative proposals to reform these areas of the law on homicide are currently gathering dust, after being rejected by the previous Labour government. The coalition are yet to state their position.